The present invention relates generally to a sensor apparatus for monitoring the presence of acetylene and hydrogen in a fluid such as, for example, an insulating fluid. More specifically, the invention relates to a sensor apparatus in which the concentration of acetylene and hydrogen dissolved in a fluid are determined by the measure of an electric current generated by electrochemical oxidation of the acetylene and hydrogen at detection electrodes.
The following will deal, by way of example only, with the detection of constituents in a fluid that may be an insulating or dielectric fluid. Electrical systems are well known in the art which use an insulating fluid as an insulating substance; these systems include for example transformers, circuit breakers and the like.
It is known that, in the event of a disturbance or malfunction of an above mentioned type of device or system, the result may be the production of one or more gases in the insulating fluid; this may occur for example if a device is working at high temperature or high conditions of electrical stress therein. Such conditions may also produce undesired moisture and/or one or more breakdown products of the dielectric material of the insulating system (i.e. insulating fluid). If such abnormal conditions are allowed to continue uncorrected, this may lead to irreparable damage to the electrical system. A timely (e.g. more or less immediate) detection and/or diagnosis of any such abnormal operation of an electrical apparatus is thus advantageous in order to be able to avoid irreparable harm to such a system.
Accordingly, various monitoring devices and systems have been proposed for the detection of any incipient failure conditions such as for example any undesired increase of the concentration of a fault gas (e.g. a combustible gas such as for example, hydrogen gas (H2), carbon monoxide gas (CO), methane gas (CH4), ethane gas (C2H6), ethylene gas (C2H4), acetylene gas (C2H2) and the like or a non-combustible gas such as for example, carbon dioxide (CO2), moisture (e.g. water or H2O), a breakdown product, contaminant substance, and/or the like contained (e.g. dissolved) in the insulating fluid.
Some such detection and/or monitoring systems are, for example, described in U.S. Pat. No. 4,112,737 (Morgan), U.S. Pat. No. 4,293,399 (Belanger et al), U.S. Pat. No. 4,271,474 (Belanger et al), U.S. Pat. No. 5,070,738 (Morgan), U.S. Pat. No. 5,271,263 (Gibeault) and U.S. Pat. No. 5,738,773 (Criddle et al.).
U.S. Pat. No. 5,738,773 for example illustrates a fuel cell arrangement for detecting oxidizable components of a gas or vapor. The fuel cell comprises first electrode means and second counter electrode means which are connected by an acidic electrolyte. The electrochemical oxidation of a fuel component in the gas results in the formation of a potential difference between the first and second electrode means; the resultant current and/or potential difference can be detected and associated with the presence and/or concentration of combustible gas detected thereby.
U.S. Pat. No. 4,293,399, for example, describes how the concentration of gaseous hydrogen dissolved in a fluid may be determined by a measure of an electric current generated by electrochemical oxidation of the gaseous hydrogen at an electrode of the detector; i.e. by a measure of a current generated in response to the presence of hydrogen (in a gas). The prior art detecting and measuring means described in this U.S. patent comprises a polymeric membrane permeable to hydrogen gas for contact with a fluid containing dissolved hydrogen gas; an electrolyte capable of facilitating oxidation of the hydrogen gas diffused through the polymeric membrane at a first electrode and reduction of an oxygen-containing gas such as air at a second electrode; and a measuring device connected to the fuel cell for measuring the intensity of the electrical current generated by the electrochemical reaction of oxidation of the hydrogen gas, this intensity being proportional to the concentration of hydrogen in the fluid.
It is advantageous for such monitoring (e.g. detection) devices, as described above, to be able to provide an accurate as possible detection and/or diagnosis of the incorrect operation of systems such as, for example, transformers, circuit breakers, shunt reactors or any electro-apparatuses using a dielectric fluid as an insulating substance such as a dielectric liquid (e.g. a dielectric oil) or a dielectric gas (e.g. SF6 gas).
A number of the above mentioned prior art monitoring devices or systems may be limited in that the sample gas received by the detector may be a mixture containing multiple gases, having a relatively low concentration of a target gas which it is desired to detect or monitor; e.g. a low concentration of acetylene gas relative to hydrogen gas. In such case, the low concentration of a target gas relative to the other gases present in a sample gas may be such that one or more of the other gases may interfere with the measurement of a predetermined target gas(es). In other words, the precision of the results of the detecting or monitoring device may thus be less than is desired; i.e. due to that fact that one or more extraneous gases may interfere with the reading of the target gas (e.g. acetylene). Another limitation of the prior art devices is that only one gas can be detected.
The presence, concentration and evolution of even very low concentrations of acetylene and hydrogen dissolved in a dielectric fluid, such as for example a dielectric oil, is a particularly useful indicator of the processes occurring (e.g. default gas production) in the insulated electrical equipment. As mentioned, in addition to acetylene and hydrogen, the dielectric fluid may contain other dissolved gases, such as carbon monoxide, ethylene, ethane, methane, etc. A reliable analysis of acetylene and hydrogen thus requires a detector having an enhanced selectivity for acetylene at very low concentrations in the presence of other such dissolved gases (e.g. hydrogen).
Accordingly, it would be advantageous to have a detector for the specific detection, measuring and monitoring of acetylene and hydrogen dissolved in a dielectric fluid (e.g., a dielectric oil used in a transformer).